The pine beetle epidemic that has ravaged Colorado’s lodgepole pine forests over the last 15 years is spreading to the ponderosa pine forests along the Front Range, including Boulder County.

In 2010, pine beetles attacked 36,000 additional acres of ponderosa pines in Boulder County, compared with 1,600 acres in 2009, according to data from the U.S. Forest Service.

Pine beetles — in moderation — are a normal part of healthy ponderosa pine forests. Researchers were not certain, at first, whether the epidemic-scale infestation in lodgepole pines would translate into an epidemic in ponderosas when the beetles crossed from the Western Slope to the Front Range, where ponderosas are more numerous.

“The beetles coming over were probably hatched in lodgepole pines, and that seemed to be what they were focused on initially,” said Maribeth Pecotte, a spokeswoman for the Boulder Ranger District. “But the bug researchers are telling us it’s in the ponderosa pine as well, and it’s at epidemic levels.”

The pine beetle infestation in neighboring Larimer County’s ponderosas has been even more widespread. In 2010, the beetles infested 181,000 acres of ponderosas, compared with 16,000 acres in 2009.

“It’s surprising how widespread the impact is on ponderosa pines in Larimer County,” said Therese Glowacki, resource management manager for Boulder County Parks and Open Space. “If Larimer County is any indication, we expect larger increases in Boulder County.”

Pine beetles tend to target the largest ponderosa pines, possibly because the thick bark helps larvae survive in the winter, according to researchers. Unlike lodgepoles, ponderosas can live to be several hundred years old.

“Probably, we will lose a lot of our mature trees,” Pecotte said.

The new infestation in ponderosas is also the driving force behind the Boulder County open space department’s aggressive forest rehabilitation projects, which include cutting large numbers of trees to create a mosaic of large openings interspersed with clumps of ponderosa pines.

“If you bring the forest density down low enough, then the remaining trees have enough resources that they are more vigorous and they have a better chance of fighting off the pine beetles,” Glowacki said. “That’s the goal of all of our restoration projects in the ponderosa pine — to give the trees a fighting chance.”

Chris Wanner, forest ecologist for the city of Boulder’s Open Space and Mountain Parks, said he has not seen large infestations in ponderosas on city land, which may be related to their relatively low elevations.

“On our property, we really haven’t seen any increased levels,” Wanner said. “It’s probably because we’re so far disjunct from existing populations — we’re not high enough and we’re not close enough to lodgepole.”

But that doesn’t mean the city’s ponderosas won’t be infested in the future.

“I think at this point, it’s kind of wait and see,” Wanner said. “We definitely have conditions that are susceptible to beetles.”

Over the last year, pine beetles have also continued to be busy in lodgepole pine forests. In Boulder County, beetles infested an additional 57,000 acres of lodgepole in 2010, compared with 46,000 in 2009.